For decades, the number of calories you ate in a day was the end of the story. Stay in a deficit, and you'd supposedly lose weight. Slip into caloric excess, and you'd gain weight. That approach worked for some people, but for others, it proved limiting, miserable, and ultimately disastrous.

And then someone finally asked the question: "What if the calorie is only the beginning of the story?"

In reaction, a dietary approach called IIFYM, or "if it fits your macros," has taken the fitness world by storm. Also known as "flexible dieting," it turns old-school, restriction-based dieting on its head by focusing instead on monitoring individual macronutrient intake. As long as you hit certain numbers, there's theoretically no limitation on what foods you can use to meet them.

Is it perfect and foolproof? Of course not. Though the basic idea of flexible dieting may seem simple, making IIFYM work as a lifestyle requires an advanced understanding of some key nutritional principles, because it can definitely be done wrong! But done right, it just might be the thing to help you stick with your plan more consistently than other approaches.

Whether you're new to the nutrition side of things, or looking for a refresher, the information below will provide you with a thorough understanding of macros, splits, and IIFYM!

If It Fits Your Macros 101

Macros, short for "macronutrients," is the term used to describe the three major (or macro) nutrients: protein, carbohydrates, and fat. Rather than placing all of your attention on counting calories or demonizing certain macronutrients, IIFYM focuses on meeting daily macro goals. Done correctly, this provides a consistent calorie intake, but one that can be personalized in endless different ways.

At first glance this may seem needlessly complicated: "Why count three different things when I can count just one?" The answer is that by emphasizing specific amounts of each macronutrient (and choosing quality sources), you can better tailor it to your lifestyle, tastes, and goals.

By focusing on macronutrients, you can tailor your nutrition plan to your lifestyle, tastes, and goals.

Imagine 2,000 calories. Hard to do, right? You could get to that number countless different ways, both unhealthy and healthy. One version of a 2,000-calorie day could help you fuel fantastic workouts, add muscle, and feel full. Another could leave you on the same-old blood sugar roller coaster, feeling cloudy and dragging butt through your training.

In other words, you need another layer of structure! Managing macros is similar to managing your monetary budget. Rather than being able to spend whatever you want as long as it hits a grand caloric total, you have to budget three different currencies—protein, carbohydrates, and fat. If you want to spend your carbs on a big pancake breakfast, you certainly can, but remember that you only have so much to spend and that you still need to hit your protein and fat totals for the day. And don't be surprised if you're hurting later that afternoon because you've spent all of your carbohydrates and are now lacking energy to power through the rest of the day.

However, the beauty of IIFYM is that you can do this very thing every once in a while and still stay on track as long as you're on point the remainder of the day. So, if you have a special occasion planned for later in the evening, you can adjust your intake throughout the day to ensure you have plenty to spend at dinner.

Meet Your Macros

When done right, IIFYM is a solid balance of moderation and flexibility. After setting your daily target macros (which we'll get to shortly), you're encouraged to consume a variety of foods to meet your goals. After all, you can get calories anywhere, but you have to get your macros from specific sources.

Build your days around these fundamental sources, and you'll have the room to indulge when necessary.

Protein

Foods containing protein

WHAT IT DOES: Protein is a combination of crucial amino acids that instigate recovery and muscle growth throughout the body. Beyond building biceps, protein promotes feelings of fullness and has been shown to be beneficial for exercising individuals looking to lose or gain weight.1-3

Foods containing carbohydrates

WHAT IT DOES: Carbs are the body's primary energy source. Both your brain and your muscles prefer to use them as fuel.

There are two types of carbohydrates: complex and simple. Complex carbohydrates digest slowly, and the foods that contain them are often darker/more brown in color. They contain an abundance of vitamins and minerals and provide a steady release of energy due to their high fiber content. Examples include oats, brown rice, starchy vegetables, and whole-wheat bread.

Simple carbohydrates digest quickly, and the foods that contain them are often lighter in color. Examples include white rice, white bread, cookies, and candy.

Fat

Foods containing fat

WHAT IT DOES: Fat is an essential nutrient involved in many bodily functions. It's crucial for cell signaling and communication in the body, it allows your body to absorb vitamins, and it promotes an optimal hormonal environment in the body. Not to mention it's delicious.

UNSATURATED FATS: These are typically regarded as the "healthiest" fats because they positively impact heart health, cognitive function, and recovery.4

SATURATED FATS: These positively influence testosterone production and optimizes hormone production in the body.

TRANS FATS: These are referred to as "bad" fats because they negatively impact heart health and increase your risk for several metabolic abnormalities.5

Flexible Dieting Versus Old-School Dieting

If you've been through the wringer of old-school dieting, it can be hard to see how IIFYM is any different than a free-for-all, but being in a caloric deficit is still crucial to losing fat, no matter where your foods are coming from. Let's compare the two methods.

Difference 1 Restrictive behaviors

Many old-school diet approaches are based around strict calorie counts, approved food lists, and sometimes complete elimination of a food or food group to lose weight (think low-fat or low-carb). This approach may work initially, but it often doesn't last.

When the dieter is feeling deprived and low-energy, a cheat meal turns into a cheat day, which turns into an eventual lack of care for the original diet. Within weeks, they end up back at their pre-diet weight, if not heavier. This is the vicious yo-yo dieting cycle.

A flexible approach avoids the mentality that certain foods are "off limits" and promotes the inclusion of a variety of foods.

IIFYM avoids the mentality that certain foods are "off limits" and promotes moderation and inclusion of a variety of foods. Rather than worrying about breaking the bank, you can indulge regularly with a bit of sweet or savory and still work toward your goal without a sense of guilt.

It's all about portion control. Dieting will still be tough, and you might still feel hungry at times, but taking a moderation-focused approach will make it a lot more bearable.

Difference 2 Athletic performance

Anyone who has ever tried to train hard while on a strict caloric-restriction plan—or one that's extremely low-carb or low-fat—knows how hard that can be. Your workouts suffer dramatically, as does your overall energy level.

Sure, abs may be ultimately "made in the kitchen," as they say, but they're also made through month upon month of high-quality training. If you want to improve your body composition in a lasting way, this is non-negotiable! Extreme caloric restriction won't get you there.

IIFYM places a focus on the importance of each macronutrient, respecting the unique role that each plays. Those who have success with it find that it enables them to feel more energized and train hard even while losing weight.

Difference 3 Social-situation success

If you've ever been on a diet that had a list—whether implied or stated outright—of "forbidden" foods, you know how even the thought of cake can make you feel guilty. Far too often, people indulge and then punish themselves later on by eating, well, nothing, or very close to it. This isn't a healthy or sustainable approach.

Following an IIFYM approach promotes less stress in these sorts of situations. You can just eat more or less of a certain macro than planned at an earlier meal. But don't forget you still have to meet your macros! It's a highly flexible system that is meant to coincide with your lifestyle and daily choices—as long as you're keeping track.

With a flexible approach to nutrition, you can have your cake and eat it, too, whether at home, a restaurant, or social gathering.

This transitions nicely to dining out, too. Restaurants often provoke anxiety in dieters due to their lack of control of portions and cooking methods. Of course, many restaurants will never be totally transparent about calories or macros, but once you've got the hang of the macro game, some back-of-the-napkin math should be enough to help you find options.

One upside of the global obesity problem is that more restaurants than ever have their nutrition available online, and some even have it on hand. Checking the menu ahead of time to determine what may fit, or what you will be spending, will allow you to enjoy your meal without worrying about getting off track.

Difference 4 The research backs up IIFYM

Multiple studies over the years have shown how ineffective the old-school restriction-based approach to dieting can be, and the stats back it up. But is IIFYM any better? It turns out that there has been research comparing old-school dieting to flexible dieting.

A study comparing the two found that people following a restrictive approach to dieting were more likely to have a higher BMI, reduced feelings of self-control, and more psychological stress related to weight and food intake.6 Chalk this up as another victory for IIFYM.

Avoiding Common Pitfalls of IIFYM

I'm not going to defend all versions of IIFYM. Plenty of people do it wrong, and they leave ample Instagram evidence of every meal along the way. This has given the approach a reputation as being unhealthy, even though it shouldn't be! I've already discussed some of these problems in my "Ask the Nutrition Tactician" column.

Pitfall 1 Missing micros

Vitamins and minerals, also known as micronutrients, are crucial for having a body that functions as well as it looks. They play crucial roles in your training and recovery, too! Unfortunately, many IIFYM adherents opt for cookies over carrots too frequently.

For optimal health and performance, don't use IIFYM as an excuse to skip veggies in favor of cookies.

Fix it: Make the conscious decision to incorporate a variety of nutrient-dense foods such as whole grains, fruits, and vegetables. They should be the norm, not the exception. In fact, I argue that you should make one serving of nonstarchy vegetables both "free" and mandatory at least three times a day.

Pitfall 2 Suboptimal protein

Sure, fatty steaks and the occasional fried food can be worked into your day, but this comes at a serious caloric cost. Additionally, if you're unintelligently sifting through plant-based proteins, you may be missing out on key essential amino acids (EAAs) necessary to promote optimal muscle growth and recovery.

Fix it: Know the difference between a complete and incomplete protein; low-quality proteins shouldn't be counted towards your total protein score. I like to use the example of peanut butter. It may have 8 grams of protein per serving, but it's an incomplete protein, meaning it's lacking in one or more of the essential amino acids. Unless you put it on some toast, or pair it with a complete protein (any protein source coming from an animal) you should be considering this only as a fat. Save your protein numbers for low-fat, high-quality sources. These are nutrient-dense and will support growth, recovery, and satiety without providing excess calories.

If you're following the vegetarian route, be sure that you're pairing complementary proteins, such as rice and beans, or choosing complete, plant-based proteins, such as quinoa and soy, to take in ample EAAs during the day.

Vegetarian meals should include complete proteins such as quinoa or tofu, or pair two complementary proteins.

Pitfall 3 Catastrophic carbohydrate choices

Similar to skimping on micros, many favor sweet sugary goodness over wholesome, fiber-rich deliciousness. I'm talking about a Snicker's bar over oats, or Skittles over an apple. They may both be carbs, but the difference is one you can feel: a short spike in energy and a subsequent crash soon after. This makes it both difficult to train effectively and to be productive throughout the day.

The result of choosing low-fiber carbohydrate options is a short spike in energy and a subsequent crash soon after.

Fix it: Don't think IIFYM is license to eat like a child. Yes, you can certainly work white bread, chips, cookies, and candies in on occasion, but they're still treats—not staples. Plan your meals out whenever possible, and design them around high-fiber carbohydrate options such as oats, brown rice, and other foods that provide a sustained release of energy. Not all carbs are equal! The source, timing, and amount all have big implications on your energy, performance, and recovery.

Pitfall 4 Lack of essential fats

Pizza, doughnuts, and ice cream sure do taste phenomenal, but if they're your only source of fat intake, we have a problem. These foods are high in certain fats, sure, but they're essentially empty of the healthy fats that can improve heart health, cholesterol levels, and help to promote a leaner body composition.7-9

Fix it: Keep your treats as treats. The rest of the time, stick to things like nuts, seeds, egg yolks, oils, and avocados to provide you with a plentiful blend of heart-healthy, recovery-supporting fats.

IIFYM for the Experienced Dieter

The longer you've been training and tracking your food, the more you know about how your body responds to certain levels of fat or carbs. However, if you want to dial in your macros to match your training and food preference, I recommend nailing down your protein and then working on finding the balance between the other two macros. Here's how that process looks:

Here are two examples, based on a 2,100-calorie plan for a 145-pound woman:

Higher-Carbohydrate Preference

Carbs 300 grams

Protein 145 grams

Fat 36 grams

Moderate-Fat Preference

Carbs 200 grams

Protein 145 grams

Fat 80 grams

IIFYM: Frequently Asked Questions

Why can't I just count calories?

Tracking calories while prioritizing healthy food sources and overall balance can definitely work! As long as you're in a appropriate deficit or surplus, your weight will gradually change. However, counting macros helps put an emphasis on each individual macronutrient, which means it can be more easily customized around individual training styles and goals.

Whatever you do, don't just cut your calories dramatically, count them, and think that's the be-all, end-all solution. For many people, solely taking a calorie-conscious approach may lead to the same old yo-yo diet trap, where they feel fatigued, deprived, and depleted. I'm sure that wasn't your plan when attempting to clean up your nutrition.

Do I need to be 100% accurate?

When it comes to calories, total accuracy is a myth. So unless you're aiming for the Olympia stage, don't sweat it. Getting within 10 grams of your target protein and carbohydrate intake is sufficient. This will allow flexibility and a much-needed relief from overanalyzing your intake.

So, if your goal is 250 grams of carbohydrates, anywhere within 240-260 grams is OK. The difference is a net change of 40 calories at most in either direction. This isn't anything to worry about.

On the other hand, fat is more than twice as calorie-dense as protein and carbohydrates, containing 9 calories per gram versus 4. To limit excess calorie consumption, aim to keep your fat intake within 5 grams of your goal. If your fat goal is 60 grams, anywhere between 55-65 grams will suffice. This, too, will result in only a miniscule net difference of 45 calories.

How do you recommend I track my macros?

Track your macros in whatever way works for you. Apps can be incredibly helpful here, many of which allow you to track your intake on the go. Most have a large nutrient and food database as well, which will allow you to find virtually any food. Some even include a barcode scanner, helping you ensure every food you eat is trackable.

Include a handful of nonstarchy vegetables three times per day.

Should I track my vegetables?

Most vegetables contain very little in the way of calories (excluding starchy veggies like peas, potatoes, and corn), so many people advocate against including them in your macros. However, they do still have calories and carbohydrates, so there's an argument to be made either way.

My recommendation is to include a handful of nonstarchy vegetables at a minimum of three meals. Don't count that amount, and do your best to consistently get it at every meal.

If you choose to have more than one serving at a meal, count the carbohydrates from the subsequent servings, to keep total calories in check. For example, 1 cup of spaghetti squash has 7 grams of carbohydrates. If you plan to have three servings at one meal, only count carbohydrates from the second and third cup. In this case, you'd count the squash as 14 grams of carbohydrates for the meal.

Should my macros be the same each day?

This is where things get personal. To keep food prep and intake as simple as possible, many experts advocate keeping macros the same, regardless of the day's training. Sure, this may save you a few minutes, but on the other hand, your caloric needs are going to be different on a rest day than on a hard training day. Does it really take that much more time to weigh out 100 grams of brown rice? Personally, I don't think so.

You probably don't need a different macro split for every day of the week, but I recommend differentiating between a training day and an off day. On days when you don't train, you will not have as great a need for carbohydrates, because you're expending far fewer calories. Cutting back on carbohydrates will help to more appropriately align your nutrition and training, particularly when weight loss is the goal. I recommend cutting back carbs by 30-50 percent, while keeping protein and fats consistent.

Sample Training-Day Nutrition

Carbs 250 grams

Protein 185 grams

Fat 70 grams

Calories 2,370

Sample Off-Day Nutrition

Carbs 125 grams

Protein 185 grams

Fat 70 grams

Calories 1,870

Once I meet my macros, should I "fill in" my remaining calories?

This happens all the time. Say your daily calorie goal is 2,500 calories, and you hit your macros with 110 calories remaining. Don't worry about "filling in" those additional calories. Focus on the macros, and the calories will even out over time.

The food options you choose each day will impact total calories consumed, but this difference varies day by day. For instance, consuming a serving of olive oil will provide you with 15 grams of fat; however, consuming 15 grams of fat from peanut butter will also provide you with trace amounts of protein and carbohydrates and about 80 extra calories. This caloric difference usually works itself out over time when including a variety of food options into your day.

In action, this means that today's slight deficit will be smoothed over by tomorrow's slight excess. There's no need to "fill in" remaining calories. The same applies if you notice you're slightly above your preset calorie goal.

Can I still have a cheat meal?

One of the major perks of following an IIFYM approach to nutrition is that you can eat a delicious combination of nutrient-dense foods and your favorite treats. So technically, you can indulge daily in a slick of cake or a piece of chocolate.

However, once in a while, it can be a nice psychological breather to not track macros for a meal. For optimal progress—specifically during a weight-loss phase—it's best to limit these "free meals" to once every few weeks or once a month.

That may sound limiting, but remember, that you can eat anything you want to every day, so long as you keep an eye on portions. That counts for plenty!

I'm confident in my starting macros and want to focus on achieving a weight-loss/weight-gain goal. How do I proceed?

Regardless of whether you're trying to lose or gain weight, your goal should be to target no more than a change in weight of 1 percent of your body weight per week to optimize the change to your body composition.

This means that a 155-pound woman focused on weight loss should aim for no more than 1.5 pounds per week, to reduce risk of muscle loss. A 170-pound male trying to gain weight should similarly aim for no more than 1.7 pounds per week, to minimize fat gain.

With this information in mind, make adjustments of 300-500 calories once your weight progress has stalled in order to keep you on pace for your goal weight change. In most cases, the best approach is to keep protein intake the same (provided it's sufficient), and manipulate carbohydrates and fat to help you tweak your numbers.

The Rest is up to You!

IIFYM isn't a set-in-stone corporate system like Atkins or Weight Watchers. It's a personal approach that's exploded in the online age, and as such, there are as many ways to approach it as there are foods in the store.

Sure, you can slip into analysis paralysis, but this approach is supposed to be enjoyable! Remember that, and remember to be honest and track faithfully, and you'll set yourself up for success. If you have more questions or have had success with IIFYM, let us know in the comments!

Always consult with a qualified healthcare professional prior to beginning any diet or exercise program or taking any dietary supplement. The content on our website is for informational and educational purposes only and is not intended as medical advice or to replace a relationship with a qualified healthcare professional.